THE PRESENT INVENTION relates to a safety-belt retractor mechanism for use in a motor vehicle, and more particularly relates to a safety-belt retractor mechanism which incorporates a locking device, which may be actuated in response to vehicle deceleration and/or extraction of the belt from the retractor with a high velocity or high acceleration, the retractor mechanism being provided with a load-limiting device which enables the belt to be pulled out to a limited extent after the locking mechanism has been actuated.
When a vehicle is involved in an accident and decelerates rapidly, an occupant in the vehicle tends to move forwardly, due to inertia. If the occupant is wearing a safety-belt associated with a typical retractor, the safety-belt retractor locks in response to the conditions that exist in such an accident situation, thus preventing more safety-belt from being paid out. The safety-belt is slightly elastic, and thus tends to decelerate the occupant of the vehicle in a gradual manner. However, in certain circumstances, for example an accident occurring at a very high speed, the force applied by the occupant of the vehicle to the safety-belt, and consequently the force applied by the safety-belt to the occupant of the vehicle, is so high that there is a risk of the occupant of the vehicle being injured by the safety-belt. Consequently, it is desirable to provide a retractor mechanism which, when subjected to a substantial force, through the safety-belt, following locking of the mechanism in an accident, permits a further length of safety-belt to be paid out, preferably against a restraining force, which may reduce the risk of injury to the occupant of the vehicle.
It has been proposed to provide a safety-belt locking mechanism which has this property, the retractor mechanism incorporating a load-limiting device which consists of a torsion bar. One end of the torsion bar is connected to the take-up spool of the retractor mechanism, on which the safety-belt is wound, and the other end of the torsion bar is connected to the means which lock the retractor mechanism relative to its housing. Such a device may permit rotation of the take-up spool through a limited angle of rotation subsequent to locking of the retractor.
To prevent an excessive stress being applied to the torsion bar, and to prevent excessive forward displacement of the belted occupant, as a result of excessive angular rotation when the take-up spool moves relative to the locking arrangement, the safety-belt retractor described in DE-A-43 31 027 is provided with a clutch inserted in the load transmission path between the take-up spool and the locking element. This locking element is engaged after the take-up spool or the torque rod has rotated a predetermined number of revolutions in the direction of withdrawal of the safety-belt. Subsequently, the torsion bar becomes inoperative. Consequently, this described arrangement is relatively complicated, and is thus expensive.
A further example of a safety-belt retractor which incorporates a torsion bar in the manner described above is disclosed in DE-A-41 27 781. In the retractor described in this Specification, an automatic locking means is provided in the form of a locking pawl which is actuated by a control system, but which is subsequently de-activated to permit rotation of the take-up spool during a phase of operation in which a load-limiting effect is provided by the torque rod. Subsequently, the spool is again immobilised by a second locking system. This locking system immobilises the spool if additional stress is applied to the system.
Thus, the prior art arrangements are relatively complicated and relatively expensive.
The present invention seeks to provide an improved safety-belt retractor mechanism.